Many materials discarded as waste retain substantial potential heating value if burned as fuel. The use of waste as fuel has two benefits: the volume of solid waste needing final disposal can be reduced, and the heat obtained can help offset demand which would otherwise drain other energy resources.
In order for suitable waste materials to find actual use as fuels, they have to be convenient to use. Only if these materials are actually used will the effort and expense of separating these materials from the general waste stream be repaid.
Two of the largest components by volume of ordinary household waste are paper and plastic (particularly polyethylene, used in food packing, plastic bags, and for many other purposes). Both paper and polyethylene are potentially suitable for use as fuels. However, waste paper and waste plastic, if used by themselves in an unprocessed form, do not burn well in such applications as fireplaces, and wood stoves and furnaces.
Stacks of paper do not burn readily. Even if paper is rolled into cylinders, combustion is difficult to sustain once the outer layers have burned away. Separating the paper into individual sheets and crumpling the sheets can be useful for starting fires, but is inconvenient for sustaining a fire; paper in this form tends to burn too hot and too quickly, with the generation of large amounts of fly ash, and the danger of burning paper scraps being drawn up the chimney.
Adding plastic directly to a fire typically results in the plastic melting into a mass which burns slowly and incompletely after dripping to the bottom of the fire.
The use of paper and other fibrous or cellulosic materials in combination with various forms of plastic materials has been suggested for various types of fuel products. U.S. Pat. No. 3,852,046 to Brown (1974) describes mixing a slurry of shredded used paper with coarse plastic ribbons and allowing the sample to dry in a board like shape, with the resulting samples being readily ignitable and capable of burning well. U.S. Pat. No. 4,220,453 to Holder (1980) uses a combination of combustible cellulosic material and a curable (thermosetting) plastic binder to form log shaped articles in a tubular mold. U.S. Pat. No. 4,326,854 to Tanner (1982) uses various combinations of cellulosic materials together with a combustible binder to form synthetic firelogs by extrusion. U.S. Pat. No. 4,810,255 to Fay and Gierke (1989) uses a primary fuel element as an inner core, covered by a combustible layer comprising a thermoplastic material and pulp fiber.
An object of this invention is to combine materials such as paper and plastic into a product which is convenient and appealing to use for fuel.
Another object of this invention is a fuel product which can be made inexpensively and without unnecessary cost to the environment.
A further object of this invention is a fuel product which can be stacked like wood logs, having a shape which when stacked provides air gaps and interior spaces between the logs to help promote combustion of the stack.